K'NEX Sky Sprinter Roller Coaster Build
I ended up getting a K'NEX Sky Sprinter Roller Coaster Building Set (paid link) as a present for my daughter and it ended up being a bit too complicated. So, dad took over. After about 4 hours I got somewhere and it ended up not being able to go around the track by itself. I put some silicon lubricant on the wheels of the little car and it still sometimes doesn't make it, but most of the time it does. This thing is almost 800 parts and over 7 feet tall. Be prepared to have some hurting fingers after snapping all of these parts together. It's worth noting I had about 5 spare parts, so the kit includes almost exactly what's needed to follow the directions. It wobbles a bit, but it's cool to see it finally running nonetheless.
Here are some more random angle pictures of the roller coaster.